ISO 639-1:2002 Codes for the representation of names of languages -- Part 1: Alpha-2 code

ISO 639-2:1998 Codes for the representation of names of languages -- Part 2: Alpha-3 code

In other words, there are two-letter codes and three-letter codes (sorted by language name in the third column!). For 22 languages exist two 3-letter-codes. The first is bibliographic (ISO 639-1/B) the second for terminological (ISO 639-2/T) use.